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Multi-User Space Link Extension (SLE) System

Wednesday, 01 May 2013

The Multi-User Space (MUS) Link
Extension system, a software and data
system, provides Space Link Extension
(SLE) users with three space data transfer
services in timely, complete, and offline
modes as applicable according to
standards defined by the Consultative
Committee for Space Data Systems
(CCSDS). MUS radically reduces the
schedule, cost, and risk of implementing
a new SLE user system, minimizes
operating costs with a “lights-out”
approach to SLE, and is designed to
require no sustaining engineering
expense during its lifetime unless
changes in the CCSDS SLE standards,
combined with new provider implementations,
force changes.

No software modification to MUS
needs to be made to support a new mission.
Any systems engineer with Linux
experience can begin testing SLE user
service instances with MUS starting from
a personal computer (PC) within five
days. For flight operators, MUS provides
a familiar-looking Web page for entering
SLE configuration data received from
SLE. Operators can also use the Web
page to back up a space mission’s entire
set of up to approximately 500 SLE service
instances in less than five seconds, or
to restore or transfer from another system
the same amount of data from a
MUS backup file in about the same
amount of time. Missions operate each
MUS SLE service instance independently
by sending it MUS “directives,” which are
legible, plain ASCII strings. MUS directives
are usually (but not necessarily)
sent through a TCP–IP (Transmission
Control Protocol–Internet Protocol)
socket from a MOC (Mission Operations
Center) or POCC (Payload Operations
Control Center) system, under scripted
control, during “lights-out” spacecraft
operation. MUS permits the flight operations
team to configure independently
each of its data interfaces; not only commands
and telemetry, but also MUS status
messages to the MOC.

Interfaces can use single- or multiple-client
TCP/IP server sockets, TCP/IP
client sockets, temporary disk files, the
system log, or standard in, standard out,
or standard error as applicable. By defining
MUS templates in ASCII, the flight
operations team can include any MUS
system variable in telemetry or command
headers or footers, and/or in status
messages. Data fields can be
arranged within messages in different
sequences, according to the mission’s
needs. The only constraints imposed are
on the format of MUS directive strings,
and some bare-minimum logical re -
quirements that must be met in order
for MUS to read the mission control center’s
spacecraft command inputs. The
MUS system imposes no limits or constraints
on the numbers and combinations
of missions and SLE service
instances that it will support simultaneously.
At any time, flight operators may
add, change, delete, bind, connect, or
disconnect.

This work was done by Toby Perkins of
Honeywell Technology Solutions Inc. for
Goddard Space Flight Center. GSC-16091-1

This Brief includes a Technical Support Package (TSP).

Multi-User Space Link Extension (SLE) System (reference GSC-16091-1) is currently available for download from the TSP library.

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